1. Field of the Invention
The present invention relates to a miniature linear motion guide device (hereinafter referred to as the miniature linear guide device) in which a bearing assembly travels linearly along a U-shaped rail member via a plurality of balls that roll in a. circulatory manner, and the manufacturing method for the device. In particular, the present invention relates to a miniature linear guide device in which one side wall, at both ends of said rail member, functions as a stopper for said bearing assembly, to prevent the assembly from sliding out of said rail member, and a method for assembling the device.
2. Discussion of the Prior Art
There has been well known in the prior art a lightweight miniature linear guide device which is made of thin plate and comprises a thin-walled, U-shaped rail member made of steel sheet which functions as a linear motion slideway, and a bearing assembly which is housed inside the U-shaped portion of said rail member and which travels reciprocally in a linear track in the longitudinal direction thereof. A bearing assembly of the type mentioned has a U-shaped slider which is also made of thin steel plate with ball-rolling grooves on the sides thereof. Within the slider, a ball-circulating member called a circulator is secured. Ball circuits which are elongated partial toroids in shape are formed in the ball-circulating member and are interconnected smoothly with the ball-rolling grooves on the slider. On the internal surfaces of the opposing walls of the U-shaped rail member, ball-rolling grooves are formed in such a manner that they face the ball-rolling grooves on the slider and a plurality of balls fills the area between the grooves and also fills the ball circuits in the circulator. As the bearing assembly travels the linear track in the longitudinal direction of the rail member, the balls roll in a circulatory motion.
Since the device features a structure in which the ball-rolling grooves on the rail member run through both ends of the rail in the longitudinal direction, and the bearing assembly itself is capable of unrestricted linear motion on the rail member, if the bearing assembly were to slide out through one end of the rail member, the balls inside would fall out and the device would come apart. In order to prevent this, in the prior art device, a means of stopping is provided on both ends of the rail member to stop the bearing assembly from sliding out of the rail member. For example, in the prior art device illustrated in FIGS. 5-7, removable plastic stopper members 2 are detachably mounted by fitting them into the ball-rolling grooves 1A near both ends of the rail member 1 to function as stoppers for the bearing assembly 3 during transportation and until the device is installed in the target instrument. Then, before the miniature linear guide device is installed in the target instrument, the stopper members 2 are removed from the rail member 1.
An example of forming stopper members as an integral part of the rail member is illustrated in FIG. 8. Here, the two ends of the bottom plate 21A of the U-shaped rail member 21 are extended outwards beyond the ends of the side plates 21B. Then the two ends of the bottom plate are bent inwards (upwards) to form an approximate L-shape and the bent sections become stoppers 22 that prevent the bearing assembly 3 from sliding out.
Generally, in miniature linear guide devices, there is a relatively large gap between the bottom plate of the rail member and the lower surface of the bearing assembly. Whereas, in the slideway between the sides of the rail member and the sides of the bearing assembly, where the balls are fitted into the ball-rolling grooves, there is very little play. The tolerances here are measured in units of .mu.m. Thus, if the miniature balls should come out, the device will not easy to reassemble. Therefore, we can say that stopping the bearing assembly from sliding out of a miniature linear guide device of this type is very important. However, with the means of stopping in the prior art, as illustrated in FIGS. 5-7, the separate removable plastic parts that are provided on the rail member as stoppers must be removed when the miniature linear guide device is installed in the target instrument. This means that, at some point during the working operation, the miniature linear guide device must be handled without stoppers. Inevitably, the bearing assembly sometimes gets separated from the rail member by mistake during this phase. Also, there is always the risk of the stoppers becoming disengaged due to vibration or the like during transportation. After the miniature linear guide device is installed in the target instrument and the motion of the bearing assembly is controlled by the drive unit of the target instrument, the means of stopping are no longer necessary. Structuring the stopper members as separate from the rail member, removable parts increases the number of parts and assembly steps, thereby increasing the cost of production.
On the other hand, with the linear guide device illustrated in FIG. 8, in which the rail member 21 and stoppers 22 are integrated as a unit, because the bearing assembly 3 is positioned with a large clearance from the rail member bottom plate 21A, as explained earlier, it is necessary to bend the ends of the bottom plate of the rail member to a considerable height in order for them to reliably function as stoppers. Also, to prevent such adverse effects as distortion of the raceway track in the rail side plate 21B at the time of the bending operation, the ends of the bottom plate must be extended greatly in the longitudinal direction, increasing the dimensions of the unit as a whole. Also, while the ends are bent upwards, the entire fiat area of the bottom plate 21A in the lateral direction must also be bent to form an L shape. Thus, the process will necessitate a press machine or another special tool. If they are bent inadequately, it may allow sliding out or cause biting in when the bearing assembly comes into hard contact with the bends.
Furthermore, with the structure mentioned above, it is not possible to assemble the device by inserting the separately assembled bearing assembly 3 in through one end in the longitudinal direction of the rail member 21 after bending the ends of the bottom plate into an L shape. With this structure, therefore, it is necessary to first divide the circulator of the bearing assembly 3 into two sections; a top part and a bottom part, and then fit them in order to the upper surface of the rail member 21. This presents the problem of increased assembly steps.